Computers have a need for the storage of binary information on different types of mediums for eventual retrieval for processing in their central processing unit (CPU). This has led to different types and speeds of storval devices, from temporary to long term storval requirements. The speed of access to the information for the various types varies widely. The major classifications of storval devices associated with computer systems are: (1) immediate-access (typically core and cache storage); (2) random access (typically RAM or other devices in which the time to obtain information is independent of the location of the information most recently obtained); and (3) sequential access (typically storval devices in which the items or information stored become available only in a one-after-the-other sequence, whether or not all the information or only some of it is desired. (Typically disk, tape or drum storage). Information can be stored as either program instructions for the computer to execute in the CPU or as data used for computations. In this patent, data will refer to both program instructions and data interchangeably.
A random access memory (RAM) is a solid state type of device manufactured from semiconductor materials that retains information only as long as the machine is running. It has the advantage of nearly instant access for the CPU (from 10 nanoseconds to 150 nanoseconds) when the data is called for. However, this type of storval has been typically very expensive in the past. For intermediate long term storage, a hard disk with a magnetic coating on its' surface can presently store data without loss for as long as ten years, with access times of 4 milliseconds to 30 milliseconds. Intermediate storval of data is data that might be required by the CPU in its daily operations on an occasional usage. For long term storage, that is, storage that requires the archiving of information, a photo-optic storval disk that uses lasers for reading the information, called a CD Rom, should store data for 100 years or more, with present access times of typically more than 200 milliseconds.
For intermediate storval of data, it has been a long sought goal to use an inexpensive system while providing a computer with faster access to data and, also, to increase the capacity for storval of data. The time for a data storval operation using a disk utilizing a sequential data transfer head means is comprised of seek, latency and command overhead times. Referring to FIG. 1, seek time is defined as the time required to position a sequential data transfer head means 180-1 above a particular track 174. The shorter distance the sequential data transfer head means 180-1 has to travel, the shorter the seek time. Referring to FIG. 3, latency time is defined as the time required for the disk 372 to rotate beneath a positioned sequential data transfer head means 380-1 until a predetermined sector of the track 374 rotates past the sequential data transfer head means 380-1. The faster the disk rotates, the smaller is the latency time.
Data storval disk controllers, the "brains" that control the devices, can pre-access the data before it is required by the CPU and store it temporarily in a data cache. The data cache is typically a RAM device that can store relatively small amounts of data. When the data needed by the computer is stored in cache, both seek and latency times are eliminated. Caching includes CPU cache, RAM cache, hard drive cache, track buffering, pre-fetching and write cache. CPU cache stores a part of a program or data so it may be accessed quickly while the CPU is executing the program. RAM cache is used for storing the most frequently accessed disk information and speeds data retrieval but limits the amount of RAM available for the program itself. RAM cache minimizes small computer system interface (SCSI) bus traffic by serving I/O requests within the computer itself. Hard drive cache is located on the controller board and is slower than RAM cache. Hard drive cache stores the most recently requested disk information and frees the computer RAM for running the program. Track buffering works on the principle that when data is requested from a particular sector, it is likely that the CPU will then require data located in adjacent sectors. In anticipation, the controller reads the entire track and stores the read data in its RAM. This speeds up information retrieval for most applications. Pre-fetching is similar to buffering except it reads the next track by a sequential data transfer head means before it is required.
Command overhead time is the time required for the computer command to be interpreted and acted upon by the data storval controller. While this is taking place, requested data stored in the called for sectors of a track may have passed beneath the sequential data transfer head means requiring the rotation of the disk means almost a full revolution before the called for sector is once again located beneath the sequential data transfer head means. Interleaving and sector skewing are used to reduce this amount of command overhead time.
The central processing unit (CPU) of some computers cannot handle data as quickly as the hard drive controller can transfer data on the spinning disk. By the time the CPU digests the information that the sequential data transfer head means has just transferred data from one sector and issue orders to the disk controller to perform another data storval operation, the predetermined sector on the spinning disk may have already passed by the sequential data transfer head means. To perform the storval of data the disk device controller controlling the sequential data transfer head means must wait a full disk rotation for that sector to once again pass beneath the sequential data transfer head means. A disk controller is a circuit that transmits and retrieves signals to the disk drive. In a personal computer a disk device controller is a printed circuit board that plugs in the expansion spot in the bus or is a printed circuit board that contains circuits that reside in or near the disk housing.
Interleaving describes how sectors are arranged on the disk, so that the device controller controlling the sequential data transfer head means can transfer data in the fastest possible sequential order. This is illustrated in FIG. 12. The information allotted to ordered sectors does not follow the sectors actual sequential numerical order; information is placed on sectors that are not physically contiguous, as can be seen from the arrows in FIG. 12. As shown in this figure, the data storval occurs first from sector 1, then from sector 10, then sector 20, then sector 30. Thus the device controller controlling the sequential data transfer head means doesn't have to wait a full rotation for the sector the sequential data transfer head means has missed to come by again.
Sector skew optimizes transferring information on adjacent tracks, in much the same way interleaving optimizes movement within a track. It does this by taking into account the time it takes the sequential data transfer head means to move to another track and the distance a sector will travel in that time (due to the disk's rotational speed), and then offsetting the numbering for the sectors on the next track.
The time for storval of a particular piece of data on a rotatably mounted disk means would be reduced if one or more of the seek, latency or command overhead times could be reduced or eliminated entirely.
A computer can presently perform a storval of data from a floppy disk in typically an average of 200 milliseconds (ms). Storval of data on a hard disk drive can presently be typically performed in less than 20 ms. However, they are both slow compared to RAM which presently can typically perform a storval of data in under 200 nanoseconds (ns). Presently a hard disk typically rotates at 3600 revolutions per minute (RPM) or greater while a floppy disk presently typically rotates at 360 RPM. Presently the majority of hard disks rotate at a constant speed and are always ready for use. A floppy disk is turned on an off thus slowing the time to access the data stored thereon.
Contemporary data transfer rates between a computer and hard disks now average from 5 to 30 megabits per second (Mb/s or millions of bits per second), i.e., 0.625 megabytes per second (MB/s) to 3.75 MB/s. Data transfer rates for floppy drives are much slower than for hard disks, varying between 0.2 to 0.4 Mb/s. Since contemporary computers can receive data at rates of 100 MB/s or more, it is readily apparent that the slow rate of transfer of data between the disk means and the processing means is effectuated by the disk storval method of sequentiality and the seeking of the proper location by movement of the sequential data transfer head means therefore creating a bottleneck in the overall rate of computer operation.
An I/O channel is the physical high speed pathway between the computer and a peripheral device. In large computers it can consist of a channel between the CPU and a peripheral device. In small computers it includes the controller and cable between the CPU and peripheral device. The channel is merely a pathway between a computer an a peripheral device or between two computers. This nomenclature may refer to the physical medium such as a coaxial cable or to a carrier frequency within a larger channel or wireless medium. In effect it is the logical or the physical connection between two different devices.
While the data is transferred from the disk in a serial sequential manner it is usually reassembled into a single byte for transferring over the I/O channel between the CPU and the disk. The more information that is available in byte form makes the I/O transfer between the device controller and the CPU occur in a more effective manner. If the system is I/O bound then this refers to an excessive amount of time for transferring data into and out of the computer in relation to the time it takes for processing within the computer. Faster I/O channels and disk drives will improve the performance of an I/O bound computer.
The present limit for the typical amount of data that can be stored on a standard 3.5" [8.9 cm] floppy disk is 4 MB, and the typical limit for a 5.25" [13.3 cm] is approximately 1.6 gigabytes (GB, one GB equals 1,000 MB). The use of magnetically coated tapes (tapes) for storing data is advantageous in that the cost of storing great quantities of data on tapes is relatively inexpensive when compared to the use of disks, but disks provide a much faster storval time for data than the tapes. Tapes suffer another drawback since the storval of data cannot be occur randomly as is the case for disks.
The amount of information that can be packed onto a disk is determined in part by the gap width of the read/write head. A narrower gap magnetizes a smaller area of the disk surface allowing the data tracks to be recorded much closer together. The gap of a typical slider is about 40 millionth's of an inch (1.02 .mu.m or micrometer) wide. Thin film read/write gaps are made by depositing layers of various materials on silicon and are only about half as wide as slider gaps and increase the storage capacity of a hard disk by nearly one third.
As shown in FIG. 1, the contemporaneous operation of disk drives involves the use of a mechanism 108, 106, 104 to position the sequential data transfer head means 180-1 over a predetermined track 174 and an electric motor 110 to rotate the disk, 172. The sequential data transfer head means positioning mechanism, which may include a stepping motor 110 as shown in FIG. 1 or a voice relay coil (or servo) 208 as shown in FIG. 2, generates heat which may create operational problems for the computer and, also, is a potential source of maintenance problems.
There are two methods for sequential data transfer head means actuator movement: A stepper motor, (the type of rotational pivot used in a floppy drive); and a servo voice-coil actuator, a more efficient and accurate method.
Stepper motors use a transmission-like system to convert an incremental rotary movement into linear travel. The motor rotates either direction a few degrees at a time; connected to it is the stepper band, which converts that incremental rotary motion into linear movement, repositioning the arm and thus changing the write/read (used interchangeably for storval) sequential data transfer head means position over the disk. These motors may experience problems with precision, known as head drift, because of normal wear and tear coupled with the unadjustable mechanical nature of the motor.
Voice coils, or servos, work like common audio speakers. The sound of a loudspeaker is determined by the strength of the current passed through its magnet, which pulls on a diaphragm connected to the speaker's cone. In a hard disk drive, the current passes through a voice-coil electromagnet, which pulls the arm toward it. The arm is held back by a spring; this provides a counter-force to the magnet that automatically moves the sequential data transfer head means back when the current is decreased. The current going to the voice coil determines the position of the sequential data transfer head means over the disk, making it infinitely adjustable.
The slightest fluctuation in the electric current can cause the sequential data transfer head means to wander away from the center of the track. To prevent this, servo data is embedded on the disk between the tracks in the form of magnetic bursts known as embedded servo or wedged servo. When sensors on the sequential data transfer head means sense that the bursts are too strong, the controller knows that the sequential data transfer head means is wandering from the center of the track and adjusts the current accordingly. Some drives place servo information at the beginning of every sector to allow for even more accuracy. Others employ doubled embedded servos, placing servo information at the beginning and middle of the sector.
Embedded servo tracks take up space on the disk and reduce its data storval capacity. Some high capacity, multiple-disk drives utilize a dedicated servo surface, in which one side of one of the disks contains only servo data, used to guide the sequential data transfer head means. The sequential data transfer head means for that surface is used solely for positioning. Because all heads are attached to the same actuator, all of the heads will be aligned and all other surfaces can be used for data.
Voice coils provides an infinite degree of positioning control; this is superior to the stepper motor, whose accuracy is limited by its incremental rotational step. By moving the sequential data transfer head means in smaller increments, the voice coil actuator can take advantage of higher density disks, which squeeze more tracks onto the same disk. They are also less susceptible to sequential data transfer head means drift. However, like in a speaker, the fabric of the cone through aging and use can become brittle, too soft, tear, etc., causing a host of different problems with age.
As shown in FIG. 1A, disks are mounted on an axle called the spindle 160. A drive may contain more than one disk, yet all disks are mounted on a single spindle. The spindle is turned by a brushless, direct drive (no gears or belts), direct-current (DC) electric motor (not shown in FIG. 1A). It may be built into the spindle, or reside below it. A flat motor below the spindle is called a pancake motor because of its flat shape. Depending on the specific drive, hard drive motors spin the disks at 3,600 RPM, which is typical, or 4,800 RPM, 5,400 RPM or 6900 RPM. With higher spindle rates comes greater noise and heat.
As previously mentioned, latency is the time it takes for a desired sector on the disk to pass underneath the sequential data transfer head means after positioning is complete by the device controller. For a disk spinning at the standard 3,600 RPM rate, average latency is 8.33 milliseconds. The faster the disk rotates, and the more data transfer heads per disk (such as shown in U.S. Pat. No. 5,010,430), the smaller the latency and the better the performance.
With the current modern hard magnetic disk storval medium, physical contact between the sequential data transfer head means and the disk must be avoided to prevent destruction of data. During operation, an air bearing created by the rotation of the disk keeps the sequential data transfer head means out of physical contact with the disk. Referring to FIG. 3, when the motor that drives the disk 372 is turned off, the sequential data transfer head means 380-1 is moved away from the active area of the disk 374 to a parking space or landing zone 338, usually located toward the center of the disk. This process is called head parking. The use of sequential data transfer head means parking reduces the chances of the sequential data transfer head means accidentally contacting the surface of the disk particularly when the unit is being transported. Elimination of accidental contact between the sequential data transfer head means and the disk is achieved through autolocking, i.e., physically locking a parked sequential data transfer head means over the landing zone.
Referring to FIG. 1, the data storval operation is performed bit by bit in a sequential manner by the magnetic sequential data transfer head means 180-1 on a circular path 174 around the disk. Referring to FIG. 4, the tracks are subdivided into sectors (like sector 444). Sectors are a logical subdivision of tracks. That is, they are a grouping of data stored on a track into separate units. This facilitates the addressing scheme for location of where the data storval is physically performed. Usually, a sector contains 4,096 bits of data, i.e., 512 bytes at 8 bits per byte stored sequentially along the direction of the track.
A sequential data transfer head means used with a disk operating at 3600 RPM has barely one thousandth (0.001) of a second to store/retrieve one sector of data. To insure that the sequential data transfer head means can keep track of its position on the disk, encoding processes have been developed. Encoding processes include timing mechanisms to correlate a disk's constant speed with the distance traveled to yield a precise calculation of the sequential data transfer head means position over the disk. Timing mechanisms include frequency modulation (FM), modified frequency modulation (MFM) and run length limited (RLL). FM requires the use of every other magnetic domain (one domain is the area required to store one bit of data, i.e., a zero and a one) to represent a clock pulse. FM uses half the disk's storval capacity for timing information. MFM moves the timing information onto a single track. MFM enables twice the magnetic data storval as FM and is known as double density recording. RLL uses a sequential data transfer head means that can create smaller magnetic domains than those used with MFM encoding. RLL also uses a code that can read 16-bit patterns of information rather than the 8-bits used by MFM. There are several RLL codes, each depends on the number of zero bits (bits are stored as zero or one) that can be stored as a consecutive string before inserting a one bit. RLL (2,7) allows two to seven consecutive bits resulting in a 50% increase in storval capacity over the standard MFM. RLL (3,9) allows three to nine consecutive bits resulting in a 100% increase in storval capacity over the standard MFM.
When data is lost, entire operations of a computer can come to a halt. Therefore, it is critical that information is archived on a regular basis in case of damage or loss to the original data. Data archiving may be achieved in a number of ways. The data may be copied onto floppy disks or backed up on a tape. Additionally, data may be saved through the use of a second hard drive which is operated either manually or with an automatic utility program. Two other ways to archive data is through disk duplexing, i.e., using one drive to duplicate the storval moves of another, and disk mirroring, i.e., using a single disk controller connected to two drives.
Several types of intermediate storval devices for storval of data have been developed within the past several years that have the advantages of floppy disks (removable storval) and the capacity of hard disks. These advances in storval mediums are known, respectively, as Winchester Removable Cartridge Drives, FIGS. 13, 13A, Bernoulli Drives, FIGS. 14, 14A, 14B, and Magneto-optic Drives, FIGS. 15, 15A.
As shown in FIGS. 13, 13A Winchester Removable Cartridge Drives are removable magnetic media drives using 5.25 inch [13.3 cm or centimeters] disk cartridges. The unit is essentially a rigid magnetically coated disk 1372 in a self contained hard plastic case (FIG. 13A) that can be inserted or removed from a chassis unit usually separate from the cpu chassis. When the cartridge is inserted, a sliding access door 1345 opens on the cartridge to allow the sequential data transfer head means 1380-1 access to the disk media 1372. The sequential data transfer head means 1380-1 floats on a cushion of air generated by the disk 1372 spinning. Thus the disk 1372 must first spin up to speed before the sequential data transfer head means 1380-1 is allowed to be moved over the disk 1372. When the encased disk is desired to be removed, first the sequential data transfer head means 1380-1 is removed from above the surface of the disk 1372 by the arm 1302, and then the disk's motor quits spinning the disk 1372. The opening of the disk then closes, and the cartridge is ejected from the drive unit. These drives are typically used for data archival, storval intensive activities and are thus popular among desktop publishing, graphic design, and multimedia persons because they can be used instead of hard drives and have the advantage of portability of information from one computer to the next. They are frequently referred to as Syquest or Ricoh cartridges, after the two main manufacturers of the cartridges. They offer data access almost as fast as some hard disk drives, and are relatively inexpensive in the speed/cost/bit comparison to other storval technologies. The do, however, suffer from questionable reliability because of the possibility of dust entering through the cartridge opening, and this increases with extensive use. They have severe shock problems of the sequential data transfer head means 1380-1 crashing onto the disk 1372 and destroying the magnetic medium of the disk 1372. This causes the disk 1372 to be unusable most of the times. The cartridges do hold a limited amount of data, dictated by the problem of fine movement of sequential data transfer head means 1380-1 and the repeatability of the location of the sequential data transfer head means 1380-1 by the arm 1304. The movement of the sequential data transfer head means is accomplished in discrete steps that is governed by the technology used for moving the arm 1304, such as a voice coil or stepper motor.
A Bernoulli drive, which uses 5.25 inch [13.3 cm] cartridges, is shown in FIGS. 14, 14A, 14B containing a flexible disk 1472 that spins within a cushion of filtered air 1454. The Bernoulli effect is observed when the velocity of a fluid, such as air, over a surface is increased and the pressure of that fluid on the surface decreases. The reduced air pressure draws the disk 1472 toward the sequential data transfer head means 1480-1, 1480-2. If a dust particle somehow enters the filter between the sequential data transfer head means 1480-1 and the disk 1472, the disk's capability to flex allows room for the particle to escape, while the filtered air 1454 blows it away. Flexing capability makes the drive less immune to a sequential data transfer head means crash (a Bernoulli drive has a shock rating of 1,000 g's). They have a similar 44/90-megabyte capacity as SyQuest units. Bernoulli drives have high reliability ratings (MTBF) as well as reasonably high marks for speed and data security. The cartridges are relatively cheap so that buying many of them will produce infinite storval capability. However, they have slightly slower speed performance than SyQuest Drives.
In FIGS. 15, 15A is shown the combination of optical and magnetic technology, the floptical media uses standard high density 31/2 inch [8.9 cm] floppy diskette technology. The housing, or cartridge, is shown in FIG. 15A. The housing has a door 1545 that slides and allows access to the medium of the disk 1572 when the cartridge is inserted. A locking tab 1546 is located on the cartridge for preventing the writing of data as a security measure. When the tab 1546 is in one particular location, the disk unit senses this and disables the writing capability of the sequential data transfer head means of the drive. As in optical discs, the servo data is perforated into the disk 1572 and then used by an optical system to locate the sequential data transfer head means. This embedded servo is indelible and so cannot be destroyed or corrupted and allows the sequential data transfer head means assembly 1558 to follow the eccentricities of the media. This increases track density from typically 135 tracks per inch [342.9 tracks per cm] to over a 1,000 tracks per inch [2540 tracks per cm]. Formatted capacity is usually 20.8 megabytes, compared to a standard floppy's 1.44 MB. The magnetic data is located in between these optical grooves. The sequential data transfer head means assembly 1558 has two different sequential data transfer head means gaps 1550, 1552: a narrow gap 1552 for use with high density floptical discs and a wide gap 1550 for use with standard floppy disks. The drive senses which type of disk has been inserted and automatically uses the appropriate gap and servo system.
A more elaborate way of archiving data is by way of a technique known as RAID (redundant array of inexpensive disks). RAID comprises three elements: a disk array controller, a collection of disks and array management software which uses algorithms to distribute data across the disks and presents the array as a single virtual disk to the host operating system. RAID requires great care in building and programming and, thus, are quite expensive. RAID offers a high degree of data capacity, availability and redundancy (except level 0 which offers no redundancy). The degree of fault tolerance varies depending on the RAID level involved. All RAID levels feature redundancy (except level 0 which divides the data into blocks and interleaves or "stripes" each block across the disk drives) and can reconstruct the data stored on any single failed disk in the array from the information stored on the remaining disks.
RAID 1 is a "mirrored disk" concept featuring duplication of each disk in the array thereby increasing reliability and availability. Since the usable storval capacity of RAID 1 is 50% of the total capacity the relative cost is high. RAID 2 is a block interleave, i.e., interleaves the data across the drives, with check disk concept. RAID 2 has excellent transfer rates for large sequential data requests but does not efficiently handle frequent, short, random disk access. RAID 3 is a byte interleave concept using a single parity disk for error recovery; it uses an array of disk drives to transfer data in parallel while one redundant drive functions as the parity disk. RAID 3 is useful when there is a need for high transfer rate and high availability. RAID 4 is a bit interleave concept using an error-correcting code; it stripes the data across the many disks at the sector level rather than the byte level. RAID 4 features a single parity drive. RAID 4 outperforms RAID 3. RAID 5 is a block interleave concept with integrated check disk; it similar to RAID 0 except it offers redundancy. RAID 5 is also similar to RAID 3 except that parity is spread over the disks, more than one drive can write concurrently and it is faster when transferring small data blocks. Where data is critical, RAID should be used. Since physical damage is expensive to repair in RAID, good maintenance must be observed and care must be taken to avoid damage to the drive.
The prior Pat. No. 5,010,430, Head Slider Arrangement For Magnetic Disk Storage Device, Yanda et. al. discloses a magnetic disk storage device having the magnetic disk with the storing reproduction region form thereon and a head slider facing the disk surface with a plurality of parallel projections to generate an air bearing. The device makes is feasible to increase the number of heads per disk and to reduce the seek distance without increasing the weight of the head actuator. It further discloses a parallel system of circular grooves that are tangent to the tracks of a disk for providing an air bearing surface. As shown by device 91, in FIG. 17 of the aforesaid patent, this air bearing is created by the airflow through the head 91 from the movement of the disk platter. Our invention differs from this concept by using a forced air flow by a forced air means to force air flow along the radial direction of the platter. The air flow of our invention causes a positive pressure of air to flow away from the heads and cause any particles of dust to be directed away from the heads instead of moving towards the heads. This makes the device of our patent a self cleaning device.
Furthermore, Pat. No. 5,010,430, in column 2 lines 3 through 9, discloses that in a conventional magnetic disk storage device the relative speed between an air bearing surface of the head slider and a rotating magnetic disk is proportionate to the distance of the center of rotation of the magnetic disk to the air bearing section. The floating force generated in the air bearing section is relatively increased as the speed raises. This is different from the device of our invention.
In addition, the invention of the Pat. No. 5,010,430 uses a head floating above the disk that is moved by an actuator arm over the proper track of information. Pat. No. 5,010,430 involves a device that positions itself over different locations on the disk platter and responds to a servo position signal as indicated in column 12 lines 25 through 35, whereas ours does not, since ours is fixed in a predetermined location.
As an additional difference Pat. No. 5,010,430 does not disclose a method of reading all 8 data bits from the 8 heads at once and does not disclose any information on how the information is retrieved or stored on the data disk platter.
U.S. Pat. No. 5,084,781 to Kamo et. al., Parallel Transfer Type Disk System, discloses a parallel transfer disk system comprising of an arrangement of a plurality of disks storing a single bit of a byte by a sequential method on a track of each said disk. Thus data is converted from parallel in the computer to serial storage on the disk. When the information is retrieved it is retrieved in a serial fashion from each disk and sent back to the computer in a parallel manner of a single byte. As a further distinction U.S. Pat. No. 5,084,781 does not disclose a mass transfer of a plurality of bytes to a single disk platter surface in a concurrent manner.
U.S. Pat. No. 5,161,137, Disk Apparatus With A Plurality Of Heads, discloses an optical disk apparatus comprising of a plurality of heads for performing erasure of information from recorded information on an optical disk. However, each of the heads is moveable and consists of a head drive system for driving the heads so as to move the heads to a target track on the disk. The apparatus of our invention differs from this patent since the data transfer head means of our invention can also be an optical switch network incorporated with a laser light source.